Bruce Fenton: The archaeology of Kangaroo Island makes it clear that humans were living there until as recently as 4000 - 2000 years ago. We do not know if these people died out or just sailed across to the mainland, as we have already established that the ancestors of Australian Aboriginals had been sailing for hundreds of thousands of years I am willing to bet that they simply sailed away from the island.
The Bradshaw images of boats do not show sails.
So maybe you mean ‘rowed away’, or ‘paddled away’ from the island? If you think there were ocean going sailing vessels hundreds of thousands of years ago then maybe you could launch a Kon-Tiki like expedition. Showing how, using only the technology available at the time, these voyages could have been made.